1. Field of the Invention
The present invention relates to a technique for converting coded images on the basis of standards such as MPEG2 and H.264.
2. Description of the Background Art
Images to be delivered on digital broadcasts, those to be stored in media such as DVDs and hard disks, and the like are compressed in accordance with various coding systems. The object for such compressions is to avoid constraint on a transmission band, increase the transmission speed, decrease the memory size or the like.
Among the coding systems that have been conventionally adopted is MPEG2. The MPEG2 is a coding system that can be used for communication media or broadcasting media, as well as for recording in storage media. The MPEG2 is widely used as an image coding system in digital broadcasts, video conferences, videophone systems or the like.
As a new standard for image coding system, an H.264 (or MPEG4-AVC) has been developed. The H.264 achieves a compression ratio twice to four times as high as that of the MPEG2.
As discussed above, there are various standards for image coding system. And there is a case where the coding system is converted for the purpose of reducing the amount of codes in a coded image that is inputted. A transcoder once decodes the inputted coded image. Then, the transcoder codes the decoded image in different coding system (or the same coding system) again.
Japanese Patent Application Laid Open Gazette No. 2006-74635 relates to a transcoder for converting an image compressed in a first compressive coding system into an image compressed in a second compressive coding system. This transcoder compresses the image in the second compressive coding system by using intermediate information which is generated in decoding the image compressed in the first compressive coding system.
By using such a transcoder to reduce the amount of codes in the supplied coded image, it is possible to decrease the size of an image to be recorded in a storage medium. Further, even when an image is transmitted to another computer or apparatus, it is possible to reduce the load on a band and speed up the processing. Thus, using the transcoder provides many merits. Though such transcoders have been developed, no specific processing method or no optimal processing technique has been suggested yet in any of inventions including one disclosed in Japanese Patent Application Laid Open Gazette No. 2006-74635.